Prior art data storage systems using rotating media divide the storage media into a concentric series of magnetic tracks known as cylinders, and a radial division of those cylinders, which are known as sectors. Each track includes separately written positional information so that reading the disk provides information on the current cylinder and sector. The time for a read-write (r/w) head controlled by an actuator to be moved over a rotating disk from a current position to a target position cylinder and sector is known as seek time. The seek time is a measurement of the latency time between when a given cylinder and sector is requested and the read/write head is located over the data of that location such that the data may be read or written. The latency or seek time to get to a random sector is on average half of the rotational time of the disk, and has a maximum value of the time for a full rotation of the disk. The radial seek time to get to a particular cylinder is governed by a servo mechanism which moves the head or plurality of heads on an actuator across the cylinders in a generally radial direction. In a typical disk drive, the rotational speed of the disk may be in the neighborhood of 7200 rpm, or 8.3 ms per rotation, while the track to track seek time is typically less than 1 ms. This causes the maximum seek time to be dominated by the rotational speed of the drive by a factor of 8 or more. While increases in rotational speed continue to occur and reduce this value, it is desired to reduce the rotational seek latency for any rotational speed.
While multiple heads on a single actuator have been used to increase storage capacity, another use for multiple head actuators is to provide independent movement of one set of heads from another, and to provide movement of independent multiple heads over the same media surface. This may be done to increase data throughput, or it may be done to provide multiple independent interfaces to the same media.
U.S. Pat. No. 4,270,154 “Head Selection Technique” by Crawford discloses the use of multiple head stacks (actuators) to improve access time and proposes multiple head positioning algorithms, but uses only one head at a time for reading or writing data.
U.S. Pat. Nos. 5,223,993 and 5,293,282 “Multiple Actuator Disk Drive” by Squires et al teach mechanical details for constructing a disk drive with multiple voice coil motor actuators and embedded servos for moving the multiple heads, while U.S. Pat. No. 5,261,058 “Multiple Microcontroller Hard Disk Drive Control Architecture”, by Squires et al discusses the use of microcontrollers for controlling a single head disk drive. However these patents do not teach or take advantage of the additional actuators to improve data throughput.
U.S. Pat. No. 5,355,486 by Cornaby describes a controller for a multiple head actuator disk drive. The controller specifically teaches a method for enabling either multiple interfaces on a single controller, or redundant writing of data from a controller interface, but does not describe a method for reducing seek latency on read or write operations.
U.S. Pat. No. 5,901,010 by Glover et al describes a two stage actuator for a ganged head system whereby a single actuator causes a primary head to track a particular cylinder of magnetic data, while a secondary head common to the primary head actuator tracks magnetic information from a cylinder on the opposite side of the primary head. This system also teaches demultiplexing and multiplexing data between two heads attached to the same actuator but does not teach demultiplexing to multiple heads on multiple actuators being positioned over the same cylinder and sector to improve seek latency.
U.S. Pat. No. 6,061,194 “Device and Method for Storing and Retrieving Original and Redundant Data” describes the reduction of seek latency by the positioning of multiple heads over the disk media, as well as recording multiple copies of data by each head. This system reduces latency at the expense of reduced recording density, since information is redundantly recorded. In addition, data write time is doubled as only a single head is used during a data write cycle.
6,121,742 by Misso describes a multiple head actuator control system for a disk drive. The system provides for variably allocating servo system bandwidth, anticipating that the head actuators are engaged in different tasks i.e. when one head is seeking and the other is idle.
U.S. Pat. No. 6,563,657 “Multiple and Reconfigurable Data Access and Storage Device using Multiple Actuators” by Serrano et al describes improved data throughput using multiple co-axial actuators as described in U.S. Pat. No. 6,121,742 described above. U.S. Pat. No. 6,563,657 uses the coaxial head actuators and a controller to reduce seek time as a single physical device, or as two independent physical devices but does not teach improved latency performance as the multiple actuators are located on the same axis.
U.S. Pat. No. 6,728,054 by Chng et al “Drive with Adaptive Data Format and Head Switch Sequencing” describes an addressing system for a disk drive for translating addresses at an interface into physical cylinder, head and sectors of the drive.
A publication by Sorin G. Stan, “Twin Actuators for Ultra-Fast Access in CD-ROM Systems” IEEE Transactions on Consumer Electronics, vol 42, No. 4, pp. 1073–1084, Nov. 1996, describes the advantages of various seek algorithms in a CD ROM system where two heads are joined by a common single actuator where the two heads move in tandem together either on the same side of the center spindle, or on opposing sides.
FIG. 1 shows a prior art disk drive and controller 100 for a two actuator system having an X channel including read/write head 118a on a movable actuator 117a and a Y channel including r/w head 118b on a movable actuator 117b. Data storage media 102 is in the form of a rotating disk having a surface which can be recorded and later read, and is driven by a spindle motor 104 under the control of a host interface controller 108. Host interface controller 108 receives read and write commands from a host interface bus 106, and each read or write command is optionally accompanied by the address of a cylinder and sector to be read or written, as will be described later. Examining the operation of the X channel, an access to a particular cylinder involves radially moving a read/write head 118a which may be located opposite a pivot point 101a on an actuator 117a, which is done by an actuator motor 116a under the control of a head servo controller 114a, which reads head positional information from the head 118a, and seeks to the desired cylinder location. When the correct sector rotates into position on a read operation, data is read serially from the r/w head 118a into the r/w amplifier controller 112a, and the data is sent to an error correction code (ECC) and memory manager 110a, which detects and corrects errors and buffers data. The error-corrected data is then presented to host interface 108 for transmission across the host interface bus 106. For a write operation, the seek operation is identical as before, and the data to be written which accompanied the seek request is transferred through the host interface bus 106 to the host interface controller 108, to the ECC 110a for generation of error correction information and buffering, and to the head r/w amplifier 112a, which may also serially encode the data to be written to the r/w head 118a on the correct cylinder and sector. In the prior art disk controller 108 which includes an independently controllable set of r/w heads 118b on a second Y channel, the identical functions are performed as were found on the X channel. Where a functional element of the X channel carried an “a” suffix on the reference numerals, the Y channel element performing the identical function carries a “b” suffix, such as actuator motor 116b, head servo controller 114b, head r/w amplifier and controller 112b, and ECC and memory manager 110b. The host interface controller 108 may control the X channel and Y channel independently as described in the prior art below, or it may control the two together to achieve a reduced seek time, as described in the prior art above.
It is desired for a disk drive having a plurality n of independently controllable head actuators which are located substantially 360/n degrees apart to operate collectively to form a single operational unit which enables n times the data throughput of a single head actuator disk system for read and write operations, and for the disk controller to provide Tseek/n seek time, where Tseek is the random seek time for a single head actuator equivalent disk controller performing the same function.
The prior art controllers describe systems which provide for increased throughput or reduced latency, but do not provide an apparatus or method for providing both.